Preparation method of artificial humic acid and carbon dioxide composite carbon fertilizer

Abstract

The invention provides a preparation method of an artificial humic acid and carbon dioxide composite carbon fertilizer. The preparation method comprises the following steps: performing low-temperature pyrolysis on biomass to obtain a volatile pyrolysis product; catalytic oxidation of volatile pyrolysis products; alkali extraction and separation of catalytic oxidation products; cO2 is introduced into a water-soluble potassium humate aqueous solution under the temperature control condition, and the composite carbon fertilizer is obtained.The method is continuously integrated at low temperature and normal pressure, the cost is remarkably reduced, pyrolysis is carried out at the temperature of 250 + / -10 DEG C, carbonation is carried out at the temperature of 50 + / -5 DEG C, operation is carried out at the normal pressure, pyrolysis-catalytic oxidation-alkali extraction-spraying-granulation-carbonation are connected in series, and high-pressure / supercritical equipment is not needed; fe2O3-CeO2 / gamma-Al2O3 improves selectivity, reduces tar and energy consumption, and is suitable for large-scale continuous production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of agricultural resource utilization and low-carbon fertilizer, and particularly relates to a preparation method of artificial humic acid and carbon dioxide composite carbon fertilizer. BACKGROUND

[0002] Under the background of agricultural green and low-carbon development goals, the preparation technology of artificial humic acid and carbon dioxide composite carbon fertilizer has become an important research direction in the fields of resources and environment and agriculture. As a natural organic macromolecular substance, humic acid has multiple functions such as improving soil structure, enhancing nutrient utilization rate and stimulating crop growth, but the natural humic acid resources are limited and the extraction process has environmental risks.

[0003] At present, the technology for preparing humic acid is faced with multiple bottlenecks: first, although the traditional high-temperature pyrolysis process (>500℃) can prepare humic acid, it will cause the rupture of the aromatic ring structure of biomass, resulting in a low yield of humic acid (usually <35%) and insufficient retention of active functional groups, and the carboxyl content is often lower than the standard requirement of ≥3.5mmol / g in the “Water-soluble Fertilizer Containing Humic Acid” (NY1106-2010). Secondly, in terms of CO2 fixation, high-pressure technologies such as supercritical method require equipment conditions of more than 15MPa, with high investment cost (>800,000 yuan / set), and the product is a single inorganic carbonate, which lacks the soil improvement function specific to humic acid. In addition, the existing technology has limited heavy metal solidification capacity, and the solidification rate of Cd, Pb and other heavy metals is generally lower than the requirement of ≥85% in the “Soil Conditioner” (NY / T3034-2016), which poses environmental risks. The traditional process such as alkali extraction also produces a large amount of high-salinity wastewater (COD>5000mg / L), causing environmental pollution.

[0004] In recent years, researchers have explored various technical paths. It is found by Northeast Agricultural University that artificial humic acid has a “double role” in rice fields, which can promote the enrichment of methanogenic microbial community and drive carbon sequestration through the Wood-Ljungdahl carbon fixation path. The “Key Technology and Industrialization of High-efficiency Biomass Pyrolysis Co-production” project in Yunnan successfully developed a high-power microwave pyrolysis equipment, which increased the production efficiency by more than 10% and reduced the energy consumption by 50-80%, providing a new solution for the utilization of biomass resources. China University of Science and Technology developed a new method of supermolecular chemical carbon capture at room temperature and pressure, which used guanidine sulfate to co-crystallize with CO2 to form stable inclusion compounds, realizing the reversible capture and release of CO2 under ambient temperature and pressure. The team of Kunming University of Science and Technology developed a green degradable controlled-release fertilizer coating material using industrial by-product gases carbon dioxide and sulfur dioxide, with a controlled-release period of 40 to 60 days, and the nitrogen utilization efficiency of crops was increased by more than 20%.

[0005] However, these technologies still have obvious limitations: CN118949649A patent attempts to couple humic acid and CO2, but still relies on commercial humic acid potassium (cost > 8000 yuan / ton), and the process is fragmented, resulting in energy consumption. The traditional method has strong dependence on raw materials, and weathered coal or commercial humic acid salt is often used, but the distribution of weathered coal resources is uneven, and the proportion of high-quality mines is low, resulting in high raw material cost and unstable supply. In addition, the existing technology lacks precise end-point control method, resulting in unstable product quality, and the cost of saline-alkali soil repair is as high as 35,000 yuan / acre.

[0006] Therefore, it is urgent to develop a new preparation technology with wide raw material sources, high efficient integrated process, low energy consumption, environmental friendliness and product multifunctionalization. SUMMARY

[0007] The present application aims to break through the triple constraints of resources, efficiency and economy by using biomass solid waste as raw material and adopting an integrated process of stepwise pyrolysis-catalytic oxidation-CO2 chelation at normal pressure, to realize the simultaneous realization of biomass high-value conversion, CO2 low-temperature and normal-pressure fixation (fixation rate ≥ 85%) and the preparation of multifunctional composite carbon fertilizer (with humic acid soil improvement and carbon fertilizer functions), and to provide an effective technical solution for agricultural carbon neutralization and soil quality improvement.

[0008] The present application uses agricultural and forestry waste biomass as raw material, and adopts the method of inert atmosphere low-temperature pyrolysis-Fe2O3-CeO2 / γ-Al2O3 catalytic oxidation in oxygen-containing atmosphere-alkali separation-spray drying-pelletizing, and CO2 carbonation of water-soluble humic acid potassium under temperature control conditions, to prepare composite carbon fertilizer with carbon sequestration and slow-release functions and humic acid-containing soil repair agent, which is suitable for soil improvement, nutrient slow-release and agricultural carbon sequestration and emission reduction applications.

[0009] Specifically, the present application provides a preparation method of artificial humic acid and carbon dioxide composite carbon fertilizer, comprising the following steps: Step S1: low-temperature pyrolysis of biomass to obtain volatile pyrolysis products; Step S2: catalytic oxidation of volatile pyrolysis products; Step S3: alkali separation of catalytic oxidation products; Step S4: under temperature control conditions, CO2 is introduced into the water-soluble humic acid potassium aqueous solution to obtain a composite carbon fertilizer.

[0010] The CO2 used is derived from industrial waste gas or bio-fermentation tail gas, and the CO2 purity is ≥ 40%; before use, it is treated by active carbon adsorption tower to remove organic impurities and molecular sieve dehydration to make the dew point ≤ -40℃.

[0011] Further, the specific step of step S1 is: crushing the biomass raw material to a particle size of ≤5 mm, drying in a drying box to a moisture content of ≤15%, and low-temperature pyrolysis in an inert atmosphere at 250±10℃ for 30 min to obtain volatile pyrolysis products.

[0012] The biomass raw material includes but is not limited to rice husk, straw, and cotton stalk.

[0013] Further, the drying adopts a staged program, 80℃ pre-drying for 30 min, and then drying at 105℃ to a moisture content of ≤15% at a heating rate of 5–10℃ / min; nitrogen is introduced during the drying process for protection, and the airflow speed is 0.5–1.0 m / s.

[0014] The nitrogen protection prevents oxidation, and too high airflow speed will cause too much biomass to be blown away, resulting in waste, and too slow airflow speed will result in slow drying speed.

[0015] Further, the inert atmosphere is nitrogen or argon, and the oxygen content is ≤100 ppm; the heating rate is 5–10℃ / min; and the volatile products generated by pyrolysis are recovered by condensation.

[0016] Further, the catalyst used for the catalytic oxidation of step S2 is a Fe2O3-CeO2 / γ-Al2O3 catalyst in which Fe2O3-CeO2 is co-supported on a γ-Al2O3 carrier.

[0017] Further, the preparation steps of the Fe2O3-CeO2 / γ-Al2O3 catalyst are as follows: A γ-Al2O3 carrier is selected, pretreated by air calcination at 450-480℃ for 2–4h, and the pore volume is measured; Fe(NO3)3·9H2O and Ce(NO3)3·6H2O are dissolved in deionized water with a volume of 0.95–1.05 times the pore volume of the carrier at an atomic ratio of Fe:Ce=3:1, the pH is adjusted to 1.5–2.0 for equal-volume co-impregnation, and then the mixture is aged at room temperature for 1–8h, dried at 80–110℃, then heated to 280–320℃ at a rate of 1–2℃ / min, kept at this temperature for 0.5–1h, and then air calcined at 460–480℃ for 3–4h to form the phase to obtain the Fe2O3-CeO2 / γ-Al2O3 catalyst; Preferably, the total oxide loading is 8–12wt%, and the impregnation can be performed twice to improve dispersion. The specific surface area of the obtained catalyst is ≥180m² / g, the pore volume is 0.35–0.45cm³ / g, and the mesopore volume fraction in the range of 2–10 nm is ≥70%.

[0018] The setting of the pore volume (0.35-0.45 cm³ / g) and the mesopore volume fraction (2-10 nm, ≥70%) is to optimize the performance of the catalyst. Moderate pore volume can provide sufficient reaction sites, both to ensure the effective adsorption and diffusion of reactants, and to avoid excessive pore volume leading to dilution of the active sites on the surface of the catalyst, thereby improving the catalytic efficiency. At the same time, the mesopore size range of 2-10 nm is moderate, which can selectively accommodate smaller molecules, improve the rate of catalytic reaction, and reduce the hindrance of large molecule reactants. Higher mesopore volume fraction (≥70%) ensures a larger specific surface area of the catalyst and sufficient reaction sites, preventing pore blockage or reduction of the active sites on the surface of the catalyst, and improving the stability and service life of the catalyst. Overall, this optimized design of pore volume and mesopore volume fraction enables the catalyst to operate efficiently and stably for a long time, improving the overall performance of the catalytic reaction.

[0019] Further, step S2 is specifically to add the volatile pyrolysis products to the Fe2O3-CeO2 / γ-Al2O3 catalyst at 5-10 wt% based on the dry biomass of the Fe2O3-CeO2 / γ-Al2O3 catalyst, under the condition of 8-12 vol% oxygen-containing gas, and catalytically oxidize at 320±15°C for 30-60 min, preferably for 45 min.

[0020] The biomass is subjected to primary pyrolysis under inert atmosphere at 250±10°C, followed by selective oxidation of the Fe2O3-CeO2 / γ-Al2O3 (Ce 4+ / Ce 3+ and Fe 3+ / Fe 2+ redox cycle; 2-10 nm mesopore mass transfer promotion), inhibiting over-combustion and heavy condensation, and enriching and generating active fragments such as carboxyl, phenolic hydroxyl, and quinone groups.

[0021] By using the Fe2O3-CeO2 / γ-Al2O3 catalyst, over-combustion and heavy condensation reactions can be effectively inhibited during the catalytic oxidation process. Over-combustion refers to the excessive involvement of oxygen during the pyrolysis of biomass, resulting in the oxidation of organic matter in the products into carbon dioxide and water, thereby losing the originally available organic matter. Heavy condensation refers to excessive polymerization reactions between pyrolysis products under high temperature conditions, which can lead to the destruction of active functional groups, thereby affecting the quality and function of humic acid. By controlling the oxygen concentration (8-12 vol%) during the catalytic oxidation stage and using the catalyst, the redox cycle of Fe2O3 and CeO2 effectively regulates the intensity of the oxidation reaction while maintaining the reaction temperature, avoiding excessive combustion and unnecessary heavy condensation reactions, thereby ensuring the quality of the volatile pyrolysis products and allowing the organic components to be better preserved.

[0022] Catalytic oxidation can also generate some important active groups, such as carboxyl (-COOH), phenolic hydroxyl (-OH) and quinone group (-C=O) and so on. The purpose of generating these active fragments is to enhance the activity of humic acid, so as to show better effect in soil improvement and nutrient release and so on. Carboxyl, phenolic hydroxyl and quinone group and other functional groups are very key active groups in humic acid, which can improve the binding ability of humic acid with metal ions or heavy metals in soil, form organic metal complex, and then promote the passivation and solidification of heavy metals, so as to reduce soil pollution. At the same time, these active groups can improve the water solubility and hydrophilicity of humic acid, improve its dispersibility and adsorbability in soil, and improve the improvement effect of soil structure. In addition, these active fragments can also promote the slow release of organic matter and nutrients in soil, so as to provide continuous nutrient supply for crops, and improve the long-term fertility and ecological function of soil. Therefore, enrichment of these active fragments is crucial to achieve the goals of agricultural carbon neutralization, soil remediation and nutrient slow release mentioned in the present application.

[0023] Further, step S3 is specifically adding 1 mol / L KOH solution to the catalytic oxidation product for alkaline extraction separation, with a solid-liquid ratio of 1:8, extracting at 80°C for 60 min; the KOH extraction process controls the pH to be 9.0-10.5, and 0.1-0.5 mol / L EDTA-2Na is added as a complexing agent, and the molar ratio of the complexing agent to heavy metal ions is 1.2-1.8:1.

[0024] The heavy metal ions refer to the heavy metal ions contained in the product after pyrolysis and catalytic oxidation of biomass raw materials (such as rice husk, straw, etc.), and the heavy metal ions include lead ions (Pb 2+ ), cadmium ions (Cd²), copper ions (Cu 2+ ), chromium ions (Cr 3+ , Cr 6+ ), zinc ions (Zn 2+ ), nickel ions (Ni 2+ ), mercury ions (Hg 2+ ), which form stable complexes with heavy metal ions by using EDTA-2Na as a complexing agent. In this application, the molar ratio of EDTA-2Na to heavy metal ions is controlled between 1.2-1.8:1, which helps to accurately capture metal ions in the solution. Subsequently, by analyzing the extract, the concentration of heavy metal ions in the solution can be detected by atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS) and other instruments. In addition, the addition of EDTA-2Na promotes the extraction and removal of heavy metal ions, and then by detecting the amount of residual metal ions, the specific content of heavy metals in the sample can be understood.

[0025] Humic-like construction and risk element passivation (alkali extraction → complexation → solidification): ionization / saponification and Aldol / Michael condensation reorganization are completed under the conditions of 1 mol / L KOH, pH 9.0-10.5, and 80℃ to form a high-activity humic acid skeleton; Aldol / Michael condensation reorganization is carried out with active fragments (such as carboxyl, phenolic hydroxyl, quinone group, and other functional groups). These active fragments are generated during the KOH extraction process under alkaline conditions, and they are recombined with other molecules or functional groups through Aldol or Michael condensation reactions to form a more active and structurally stable humic acid skeleton. This process helps to improve the functionality of humic acid and the soil improvement effect. EDTA-2Na complexation transfers free metals, and the supernatant is purified; the residual metal is solidified by (hydro) oxide, carbonate, and organic complex in the form of mineral ash + granulation, constructing a porous slow-release carrier.

[0026] Further, the supernatant after alkali extraction is spray dried to obtain water-soluble potassium humate, and the residue is granulated to obtain a soil remediation agent; the spray drying conditions are: inlet temperature 180-190℃, outlet temperature 85-90℃, and atomization pressure 0.8-1.2MPa; the particle size distribution of the obtained potassium humate powder is D50=45-55μm, and the water solubility is ≥95%. During the granulation process, 10-20% of a binder is added, and the binder is selected from one or a combination of carboxymethyl cellulose sodium and polyvinyl alcohol; the particle size of the product after granulation is 2-4mm, and the compressive strength is ≥15N.

[0027] Further, the reaction endpoint of step S4 for preparing the composite carbon fertilizer is determined by the following multiple indicators: (i) solution conductivity ≥15mS / cm; (ii) pH drops to 7.2-7.8; (iii) bicarbonate (HCO3 – ) concentration reaches 120-150mmol / L, and the prepared composite carbon fertilizer has performance indicators of CO2 fixation rate ≥85% and nutrient release period ≥30d.

[0028] Inorganic-organic "double carbon" synergistic fixation and slow release (carbonation compounding): 10% K-humic acid solution is blown with CO2 at 50±5℃ to form a soluble carbon pool mainly composed of HCO3 – / KHCO3, which is associated / multi-point coordinated with humic acid anions to form micro-clusters, achieving ≥30d carbon and nutrient slow release after entering the soil; the endpoint criteria are conductivity ≥15mS / cm, pH 7.2-7.8, and [HCO3 – ]=120-150mmol / L.

[0029] Compared with the prior art, the present application has the following outstanding features and advantages: 1. The invention is continuously integrated at low temperature and normal pressure, with significant cost reduction: pyrolysis at 250±10℃, carbonation at 50±5℃ and normal pressure operation, in series "pyrolysis-catalytic oxidation-alkali extraction-spraying-granulation-carbonation", without high pressure / supercritical equipment; Fe2O3-CeO2 / γ-Al2O3 improves selectivity, reduces tar and energy consumption, suitable for large-scale continuous production.

[0030] 2. Outstanding product performance, carbon sequestration and fertilizer effect: water-soluble potassium humate index is stable (humic acid ≥50%, solubility ≥95%); composite carbon fertilizer CO2 fixation rate ≥85% under mild conditions, nutrient / inorganic carbon slow release ≥30d; achieve "one line multi-product" (water-soluble potassium humate, soil repair agent, composite carbon fertilizer) synergistic value-added.

[0031] 3. Environmental safety and controllable amplification: KOH-EDTA complexation + residue granulation solidification, Cd / Pb solidification rate ≥85%; conductivity / pH / HCO3 – As a triple endpoint to achieve stable quality; raw materials and CO2 sources are broad-spectrum and reduce high-salt wastewater and tar emissions, facilitating standardized amplification landing. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is the overall process flow chart of Example 1; Figure 2 is the schematic diagram of the integrated device of low-temperature pyrolysis and catalytic oxidation of Example 1; Figure 3 is the schematic diagram of the preparation process of the catalyst of Example 1; Figure 4 is the XRD test chart of the catalyst of Example 1; Figure 5 is the H2-TPR and O2-TPD characterization curve of the catalyst of Example 1; Figure 6 is the composition comparison chart of the pyrolysis product before and after catalytic oxidation of Example 1; Figure 7 is the schematic diagram of the alkali extraction-complexing purification process and the heavy metal removal / solidification effect curve of Example 1; Figure 8 is the spray drying particle size distribution and solubility performance chart of Example 1. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application. The technical solutions of the present application will be further described below with reference to the embodiments.

[0034] In the following examples and comparative examples, the humic acid content is determined by elemental analysis or acid-base titration, and the organic component analysis is performed using a PerkinElmer 2400 series elemental analyzer. The K2O content is determined by ICP-OES (Thermo Scientific iCAP6000 series) to ensure the accuracy of the potassium content. Water-insoluble substances are determined by drying or filtration method, and the weighing is performed using a Mettler Toledo precision balance; the water solubility is determined by filtration and weighing method, and Whatman filter paper and Mettler Toledo AG245 precision balance are used. The particle size D50 is determined by laser particle size analysis method, and accurate particle size distribution data are obtained using a Malvern Mastersizer 3000 laser particle size analyzer. These measurement means ensure the quality control of the product and provide accurate data support for the subsequent production process.

[0035] Specific surface area (BET method) test: The specific surface area is determined by gas adsorption experiment (using nitrogen). By measuring the adsorption amount of nitrogen on the surface of the catalyst and applying the BET (Brunauer-Emmett-Teller) formula, the specific surface area of the catalyst can be calculated. This specific surface area reflects the number of active sites on the surface of the catalyst, and is closely related to the catalytic activity of the catalyst.

[0036] Pore volume (BJH method) test: The pore volume is determined by gas adsorption-desorption experiment, especially by BJH (Barrett-Joyner-Halenda) method. This method is based on the nitrogen adsorption-desorption curve to analyze the pore structure of the catalyst and calculate the pore volume, especially the volume of micropores and mesopores. The size of the pore volume affects the reaction performance of the catalyst, and a larger pore volume can provide a larger surface area and more reaction sites.

[0037] Mesopore volume fraction determination: Mesopore volume fraction is usually obtained in the pore size distribution analysis. The pore size distribution of the catalyst is obtained by gas adsorption experiment (such as nitrogen adsorption), and the pore volume fraction in the range of 2-10 nm is calculated. The mesopore volume fraction directly affects the catalytic efficiency of the catalyst, especially in catalytic oxidation reactions, because mesopores can provide a good reaction and mass transfer environment.

[0038] XRD phase analysis was performed on an X-ray diffractometer (Rigaku SmartLab) equipped with a Cu Kα ray source (λ = 1.5418 Å), with the following specific test conditions: tube voltage 40 kV, tube current 40 mA, using continuous scanning mode, scanning range 2θ = 20°-80°, scanning speed 2° / min, step width 0.02°, counting time 0.5 s per step, using graphite monochromator filtering, and detector being a scintillation counter; before testing, the powder sample was uniformly filled in the glass sample holder slot and fixed by pressing with a glass slide, and after obtaining the diffraction pattern, the phase identification was performed by comparing the PDF standard card through Jade software.

[0039] O2-TPD test was performed on a system of chemisorption analyzer (Micromeritics AutoChem II) combined with mass spectrometer (monitoring m / z = 32 signal), with the following specific steps: 100 mg of 40-60 mesh catalyst sample was accurately weighed and placed in a U-shaped quartz reaction tube, under 5% O2 / He mixed gas (flow rate 20 mL / min) atmosphere, the sample was programmed to heat from room temperature to 500℃ at a rate of 10℃ / min and kept constant for 60 minutes, to complete the deep oxidation of the catalyst surface and the removal of carbonate impurities; then the sample was cooled to 50℃ under the same oxygen atmosphere and continuously aerated for 30 minutes to reach adsorption equilibrium of active oxygen species; then high-purity helium gas (flow rate 40 mL / min) was switched on and purged at 50℃ for 60 minutes to completely remove physically adsorbed oxygen; finally, the sample was programmed to heat from 50℃ to 800℃ at a rate of 10℃ / min under helium atmosphere, and the O2 desorption signal was continuously recorded by mass spectrometer to obtain the desorption characteristic spectrum of active oxygen species with different bonding strengths on the catalyst surface.

[0040] H2-TPR test was performed by using a chemisorption analyzer (Micromeritics AutoChem II 2920): 50.0 mg of the 40-60 mesh catalyst sample was accurately weighed and placed in a U-shaped quartz reaction tube, first heated from room temperature to 300℃ at a temperature rise rate of 10℃ / min under an atmosphere of ultra-high purity argon (flow rate 30 mL / min) and kept constant for 30 minutes to completely remove the surface physical adsorption of impurities; then cooled to 50℃ under argon protection, the gas flow was switched to 5% H2 / Ar mixed gas (flow rate 20 mL / min), and when the thermal conductivity detector (TCD) signal was stable, the temperature was programmed to rise from 50℃ to 800℃ at a rate of 10℃ / min, while the TCD continuously monitored the change of hydrogen concentration; finally, by analyzing the hydrogen consumption peak area in different temperature intervals, combined with standard substance calibration, the total hydrogen consumption was calculated, and the quantitative reduction characteristic data of the reduction peak in the range of 350-450℃ was obtained.

[0041] Example 1 With reference to Figure 1 , the present embodiment provides a preparation method of artificial humic acid and carbon dioxide composite carbon fertilizer, comprising the following steps: Step S1: The air-dried rice husk is crushed to a particle size of ≤5 mm, pre-dried at 80℃ for 30 min, and then dried at 105℃ to a moisture content of ≤15%, with a temperature rise rate of 5℃ / min; and under the protection of N2 (flow rate 0.8 m / s, oxygen content ≤100 ppm) atmosphere, heated to 250℃ at a temperature rise rate of 5℃ / min in a tube furnace and kept for 30 min for low-temperature pyrolysis; with reference to Figure 2 , the low-temperature pyrolysis and catalytic oxidation integrated device is composed of a tube furnace, a gas control unit, a catalytic bed, a condensation recovery system and the like. The biomass raw material completes low-temperature pyrolysis under nitrogen protection, and the volatile products obtained immediately enter the downstream catalytic oxidation reaction section, avoiding secondary condensation and excessive coking phenomenon, and improving the retention rate of active functional groups.

[0042] Step S2: Then 10 vol% oxygen-containing gas is introduced, and Fe2O3-CeO2 / γ-Al2O3 catalyst is introduced for 45 min at 320℃ for catalytic oxidation, the total loading of the catalyst used is 10wt%, the specific surface area is 196 m² / g, the pore volume is 0.41 cm³ / g, and the mesopore volume fraction is 73% in the range of 2-10 nm. The effect of catalytic oxidation is as shown in Figure 6As shown, after this step, the dichloromethane extract of pyrolysis condensate was filtered through a 0.22 pm microporous filter, and then analyzed using an Agilent 7890B / 5977A GC-MS system; the chromatographic separation used an HP-5MS capillary column (30 m x 0.25 mm x 0.25 pm), with high-purity helium as the carrier gas at a flow rate of 1.0 mL / min, using a splitless injection mode with an injection port temperature of 280°C; the programmed temperature was set to an initial 50°C for 2 minutes, then increased to 300°C at a rate of 10°C / min and maintained for 5 minutes; the mass spectrometry interface temperature was 280°C, the ion source temperature was 230°C, the electron impact ionization energy was 70 eV, and the mass scan range was m / z 35-550. Under these optimized conditions, the components were effectively separated and identified, and finally the tar content was significantly reduced from about 60% to about 20%, while the content of light oxygenated compounds, which are key precursors of humic acid, was significantly increased from about 20% to about 40%. This transformation directly proves that the catalytic oxidation process effectively inhibits the generation and excessive condensation of tar, and selectively enriches intermediate products rich in active functional groups such as carboxyl and phenolic hydroxyl groups, laying a solid foundation for subsequent alkaline extraction to prepare high-activity humic acid.

[0043] Step S3: The condensate and the coke powder (the condensate is derived from the condensation of the catalytic oxidation product in S2, and is the main effective component source for preparing water-soluble potassium humate. The coke powder is derived from the solid residue of pyrolysis in S1, which does not participate in the gas-phase catalytic oxidation reaction in S2) were subjected to alkaline extraction with 1 mol / L KOH (solid-liquid ratio 1:8) at 80°C for 60 min, and then complexed with 0.2 mol / L EDTA-2Na (molar ratio to heavy metals 1.5:1). After centrifugation, the supernatant was spray dried (inlet temperature 185°C, outlet temperature 88°C, atomization pressure 1.0 MPa) to obtain 132 g of water-soluble potassium humate powder, with a humic acid content of 52.6%, a K2O content of 10.8%, water-insoluble matter of 1.2%, a water solubility of >95%, and a particle size of about 50 pm. D 50 The determination of the key process parameters (pH 9.0-10.5 and the addition of EDTA-2Na) in this step is based on the data shown in the accompanying Figure 7 The broken line graph clearly shows that the removal rate of heavy metals increases with increasing pH; under the same pH conditions, the use of EDTA can systematically and significantly improve the removal rate. This rule directly verifies the scientificity of controlling the alkaline extraction pH at 9.0-10.5 and adding EDTA-2Na, which ensures efficient complexation of free heavy metal ions and is the key guarantee for achieving a supernatant that is deeply purified and a final product with a Cd / Pb solidification rate of >85%. The particle size distribution characteristics of the potassium humate powder are shown in Figure 8As shown, its single peak distribution curve indicates that the product particle size is concentrated, with a D50 value of about 50 μm, which is consistent with the results measured by the laser particle size method, which directly verifies the effectiveness of the above-mentioned spray drying process parameters. The optimized particle size distribution ensures that the product has good flowability and high water solubility, providing physical protection for the implementation of spray irrigation, drip irrigation and other water and fertilizer integrated applications. The residue was added to 15% sodium carboxymethyl cellulose (CMC-Na) to form granules, obtaining 418 g of the repair agent, which had a humic acid content of 36.4%, an organic matter content of 48.7%, a pH of 8.2, a particle size of 2-4 mm, and a compressive strength of 19.6 N (at room temperature, using a particle strength tester (Instron 3345 type single column bench tester) to complete, the specific process is as follows: first, 15% sodium carboxymethyl cellulose (CMC-Na) is used as a binder to granulate, and the complete repair agent granules in the size range of 2-4 mm are strictly sieved to randomly sample 30, which are placed in turn on the horizontal test platform of the instrument; then start the test program, make the cylindrical probe with a diameter of 5 mm vertically downward at a constant loading rate of 1 mm / min, monitor the pressure change throughout the process until the granule breaks, and record the peak pressure at the moment of breakage; finally, calculate the average value of all effective test data). This result proves that the mechanical stability of the granules meets the requirements of practical applications.

[0044] Step S4: The obtained potassium humate solution was dissolved into a 10% solution, and treated CO2 (concentration ≥ 40%, dew point ≤ -40℃) was blown in at 50℃ for 2h, reaching the triple end point indicators (conductivity 15.8 mS / cm, pH 7.5, [HCO3 – ]=135 mmol / L). The final composite carbon fertilizer CO2 fixation rate reached 86.9%, the nutrient release period was ≥ 34d, and the heavy metal Cd / Pb solidification rates were 90.3% and 91.5%, respectively.

[0045] Determination of CO2 fixation rate: first, potassium humate was prepared into a 10% aqueous solution as a reaction substrate, which was placed in a reactor with a constant temperature jacket to maintain 50±0.5℃; a pre-treated CO2 gas with a concentration of 40% (ensured dew point ≤ -40℃ by a double-stage condensation dehydration device) was blown into the reaction solution at a flow rate of 0.8 L / min controlled by a mass flow meter, and the reaction was continued for 120 minutes; during the process, online conductivity meter (Mettler Toledo FiveGo F4) and pH meter (Mettler Toledo FE28) were used to monitor the solution parameters in real time, and automatic potentiometric titrator (Metrohm 902 Titrando) was used to determine HCO3 – concentration at regular intervals; when the system simultaneously reached conductivity 15.8 mS / cm, pH 7.5 and HCO3 –The reaction was terminated at a triple end point of 135 mmol / L, and the unreacted carbonate content was finally determined by titration.

[0046] Determination of nutrient slow-release period: 1.000 g (accurate to 0.0001 g) of the fertilizer sample with a particle size of 2-4 mm was accurately weighed into a 250 mL conical flask with a stopper, 200.0 mL of deionized water was added, and after sealing, it was placed in a constant temperature shaking incubator at 25.0±0.5°C and continuously shaken at a frequency of 120 rpm; samples were taken at 1, 3, 7, 14, 21, 28, 34 days, respectively, and 3 parallel samples were taken each time. When sampling, a 0.45 μm water microporous filter membrane was used for rapid filtration separation, and the filtrate was immediately determined for potassium ion concentration using an ion chromatograph (equipped with an IonPac CS12A chromatographic column, a conductivity detector, and a 20 mM methanesulfonic acid solution as the eluent, a flow rate of 1.0 mL / min). The time required for nutrient release to reach 80% was determined by the cumulative release curve, and the experimental data showed that the cumulative release rate of potassium ion did not reach the threshold value by the 34th day, so it was determined that the fertilizer had a long-acting slow-release property of ≥34 days.

[0047] Reference Figure 3 The preparation method of the Fe2O3-CeO2 / γ-Al2O3 catalyst used in step S2: First, γ-Al2O3 was selected as the carrier and was subjected to air calcination treatment at 500°C for 3 hours to remove impurities and provide a suitable surface structure for subsequent metal impregnation. On this basis, Fe(NO3)3·9H2O and Ce(NO3)3·6H2O were dissolved in deionized water according to an atomic ratio of Fe:Ce of 3:1, and the solution volume was controlled at 1.05 times the pore volume of the carrier to ensure that the metal precursors could fully cover the surface of the γ-Al2O3 carrier. Subsequently, the solution was adjusted to a pH of 2.0 and subjected to an aging reaction at room temperature for 5 hours. Next, the obtained precipitate sample was dried at 100°C, and then heated to 320°C at a heating rate of 2°C / min and held for 1 hour, followed by heating to 480°C and air calcination at this temperature for 3 hours. Figure 4 The X-ray diffraction (XRD) pattern of the catalyst. As can be seen, there are multiple obvious diffraction peaks in the range of 2θ=28°-55°, indicating that the active components in the catalyst have been successfully loaded and formed a relatively stable crystal structure. These crystal phases help to improve the activity and stability of the catalyst at low temperatures. Figure 5The H2-TPR and O2-TPD characterization results of the catalyst are shown. Among them, the H2-TPR curve (orange) has a reduction peak in the range of 350-450℃, indicating that the catalyst has good reducibility and the active component is easy to be activated; the O2-TPD curve (blue) has an oxygen desorption peak in the range of 300-600℃, indicating that there are abundant active oxygen species on the surface of the catalyst, which can effectively promote the decomposition and conversion of small organic molecules in the catalytic oxidation reaction. Therefore, the catalyst has strong reducibility and surface active oxygen reserve capacity, which helps to improve the catalytic oxidation efficiency of low-temperature pyrolysis products.

[0048] Example 2 The present embodiment provides a preparation method of artificial humic acid and carbon dioxide composite carbon fertilizer. The specific steps refer to Example 1, and the difference between the present embodiment and Example 1 is that corn straw is used instead of rice husk for the experiment, and 8vol% oxygen-containing gas is used for the catalytic oxidation stage at 330℃ for 45min. The spray drying conditions of the extract are inlet temperature 190℃, outlet temperature 90℃, and atomization pressure 1.2MPa; and 20% polyvinyl alcohol (PVA) is used as the binder in the granulation stage. The obtained potassium humate has a yield of 145g, a humic acid content of 51.1%, K2O of 10.2%, and water solubility ≥96%; the residue granulation repair agent has a humic acid content of 35.2%, organic matter of 46.9%, and compressive strength of 22.4N (particle size 2-4mm). The 10% aqueous solution of potassium humate is introduced into CO2 for 2h at 50±5℃, and the final conductivity is 16.1mS / cm, pH is 7.4, and [HCO3 – ] is 132mmol / L. The CO2 fixation rate of the composite carbon fertilizer is 88.1%, and the release period is ≥36d; the Cd / Pb solidification rates are 88.7% and 89.9%, respectively.

[0049] Example 3 The present embodiment provides a preparation method of artificial humic acid and carbon dioxide composite carbon fertilizer. The specific steps refer to Example 1, and the difference between the present embodiment and Example 1 is that 10kg of rice husk and cotton stalks are mixed in a dry mass ratio of 7:3 instead of rice husk for the experiment, and a continuous rotary furnace is used to complete the low-temperature pyrolysis under nitrogen protection at 260℃ for 30min; the O2 concentration of the gas used in the catalytic oxidation stage is 9vol%, and the gas hourly space velocity (GHSV) is 2500h -1, reaction temperature 335℃, Fe2O3-CeO2 / γ-Al2O3 catalyst 6kg. The resulting volatile product was reacted with 1 mol / L KOH at a solid-liquid ratio of 1:8 at 80℃ for 60 min, and 0.2 mol / L EDTA-2Na (molar ratio 1.4:1) was added for complexation. The spray drying conditions were the same as in Example 1, and the granulation binder was a composite of 12% CMC-Na and 5% PVA. Carbonation was carried out by blowing fermentation tail gas (CO2 concentration 55%, dew point ≤-40℃) treated with activated carbon and 3A molecular sieve at 55℃ for 2h. The dry basis product mass balance was: humic acid potassium 1.38kg, accounting for 13.8%; repair agent 4.32kg, accounting for 43.2%, with a system closure error of not more than ±3%. The product indicators were stable: humic acid potassium contained 53.0% humic acid, K2O content 10.5%, water insoluble 1.5%, particle size D 50 50μm; composite carbon fertilizer CO2 fixation rate 87.4%, slow-release period ≥35d; repair agent humic acid 35.8%, organic matter 47.5%, compressive strength 18.7N. After 5 batches of continuous operation, the end point indicators of conductivity, pH, [HCO3 – ] were in good consistency, with batch-to-batch RSD of 3.2%, 2.4%, 4.1% respectively. The specific surface area of the catalyst decreased from 196m² / g to 188m² / g after 40h of operation, with an activity retention rate >95%, verifying the stability and scale-up adaptability of the process.

[0050] Comparative Example 1 This comparative example provides a method for preparing an artificial humic acid and carbon dioxide composite carbon fertilizer. The specific steps refer to Example 1, and the difference between this comparative example and Example 1 is that no Fe2O3-CeO2 / γ-Al2O3 catalyst is added and no catalytic oxidation treatment is carried out. Subsequently, alkali extraction, spray drying and CO2 carbonation treatment are carried out according to Example 1. The test results show that the humic acid content in the obtained humic acid potassium product is 33.6%, the water-soluble proportion is 67.4%, and the carboxyl functional group content is only 2.02mmol / g; the CO2 fixation rate is 61.3%, and the product nutrient release period is less than 20 days. Compared with Example 1 (humic acid content ≥50%, carboxyl content 3.9mmol / g, CO2 fixation rate ≥85%, nutrient release ≥30d), this comparative example lacks the catalytic oxidation step, resulting in incomplete aromatic structure and severe loss of functional groups, and the carbon fixation efficiency decreases significantly.

[0051] Comparative Example 2 The comparative example provides a preparation method of artificial humic acid and carbon dioxide composite carbon fertilizer. The specific steps refer to Example 2. The straw is used as raw material, crushed and dried, pyrolyzed at 550°C for 45 min under inert atmosphere, and other operations are the same as Example 2. The pyrolysis product is obtained by alkali extraction and spray drying to obtain potassium humate. The test results show that the yield of potassium humate obtained by this method is 28.1%, the humic acid content is 31.5%, the water solubility is 58%, the carboxyl content is 1.87 mmol / g, the humic acid color is dark brown and black, and the coking state is obvious. Compared with the potassium humate obtained in Example 2 (humic acid content 52.6%, carboxyl content 4.0 mmol / g), the pyrolysis temperature in this comparative example is too high, causing the cracking and coking of aromatic structure, the serious damage of active functional groups, and the obvious decrease of humic acid quality.

[0052] Comparative Example 3 The comparative example provides a preparation method of artificial humic acid and carbon dioxide composite carbon fertilizer. The specific steps refer to Example 3. A commercially available potassium humate product (humic acid content > 50%, price about 8500 yuan / ton) is used to prepare a 10% aqueous solution, which is reacted in a 15 MPa supercritical CO2 environment at 40°C for 2 h. Other steps are the same as Example 3. It is found that the HCO3 – concentration in the product of this process is 115 mmol / L, the CO2 fixation rate is about 72.8%, the nutrient release period is about 25 days, but the high-pressure equipment investment is high, the energy consumption is about 4.6 GJ / tCO2, the unit cost increases significantly, and it does not have the heavy metal passivation function. In comparison, Example 3 uses CO2 fixation under normal pressure, the fixation rate is increased to 87.5%, the release period is extended to 34 days, the process energy consumption is significantly reduced, the equipment cost can be reduced by about 70%, and at the same time it has the functions of heavy metal solidification and soil remediation.

[0053] Comparative Example 4: No addition of complexing agent for heavy metal treatment The comparative example provides a preparation method of artificial humic acid and carbon dioxide composite carbon fertilizer. The specific steps refer to Example 1. In this example, cotton stalks are used as raw material, and pyrolysis, catalytic oxidation and alkali extraction are carried out according to Example 1, but no EDTA-2Na complexing agent is added. The subsequent steps are consistent with Example 1. Analysis shows that the Cd residue in the obtained potassium humate is 6.2 mg / kg, the Pb residue is 22.7 mg / kg, and the Cd / Pb solidification rate in the soil remediation agent is 62.1% and 64.4%, respectively. In comparison, after adding EDTA-2Na in Example 1, the Cd / Pb solidification rate is > 85%, the heavy metal risk of the product is significantly reduced, and it meets the NY / T3034-2016 standard. It is shown that the complexing agent step is key to the control effect of heavy metals, and the omission of this step will greatly reduce the environmental safety.

[0054] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. A method for preparing a compound carbon fertilizer of artificial humic acid and carbon dioxide, characterized in that, Includes the following steps: Step S1: Low-temperature pyrolysis of biomass yields volatile pyrolysis products; Step S2: Catalytic oxidation of volatile pyrolysis products; Step S3: Alkali extraction and separation of catalytic oxidation products; Step S4: Under controlled temperature conditions, CO2 is passed into a water-soluble potassium humate aqueous solution to obtain a compound carbon fertilizer.

2. The method for preparing the artificial humic acid and carbon dioxide compound fertilizer according to claim 1, characterized in that, The specific steps of step S1 are as follows: crush the biomass raw material to a particle size ≤ 5 mm, dry it in a drying oven to a moisture content ≤ 15%, and then perform low-temperature pyrolysis at 250±10℃ for 30 min in an inert atmosphere to obtain volatile pyrolysis products.

3. The method for preparing the artificial humic acid and carbon dioxide compound fertilizer according to claim 2, characterized in that, The drying process was carried out in stages: pre-drying at 80℃ for 30 min, followed by drying at 105℃ until the moisture content was ≤15%, with a heating rate of 5–10℃ / min; nitrogen gas was introduced for protection during the drying process, with an airflow velocity of 0.5–1.0 m / s.

4. The method for preparing the artificial humic acid and carbon dioxide compound fertilizer according to claim 2, characterized in that, The inert atmosphere is nitrogen or argon, with an oxygen content ≤100ppm; the heating rate is 5–10℃ / min; the volatile products generated by pyrolysis are recovered by condensation.

5. The method for preparing the artificial humic acid and carbon dioxide compound fertilizer according to claim 1, characterized in that, The catalyst used for catalytic oxidation in step S2 is a Fe2O3–CeO2 / γ-Al2O3 catalyst co-supported on a γ-Al2O3 support.

6. The method for preparing the artificial humic acid and carbon dioxide compound fertilizer according to claim 5, characterized in that, The preparation steps of the Fe2O3–CeO2 / γ-Al2O3 catalyst are as follows: γ-Al2O3 support was selected, pretreated by air calcination at 450-480℃ for 2–4 h, and the pore volume was measured. Fe(NO3)3·9H2O and Ce(NO3)3·6H2O were dissolved in deionized water with an atomic ratio of Fe:Ce=3:1, in a volume of 0.95–1.05 times the pore volume of the support. The pH was adjusted to 1.5–2.0 and the mixture was co-impregnated in equal volumes. After aging at room temperature for 1–8 h, the mixture was dried at 80–110 °C. The temperature was then increased to 280–320 °C at a rate of 1–2 °C / min and held for 0.5–1 h. Finally, the mixture was calcined in air at 460–480 °C for 3–4 h to form the Fe2O3–CeO2 / γ-Al2O3 catalyst.

7. The method for preparing the artificial humic acid and carbon dioxide compound fertilizer according to claim 1, characterized in that, Step S2 specifically involves adding 5–10 wt% Fe2O3–CeO2 / γ-Al2O3 catalyst (based on dry biomass) to the volatile pyrolysis products under a gaseous condition containing 8–12 vol% oxygen, and catalytically oxidizing them at 320±15℃ for 30–60 min.

8. The method for preparing the artificial humic acid and carbon dioxide compound fertilizer according to claim 1, characterized in that, Step S3 specifically involves adding 1 mol / L KOH solution to the catalytic oxidation product for alkaline extraction and separation, with a solid-liquid ratio of 1:8, and extracting at 80℃ for 60 min; the pH is controlled at 9.0–10.5 during the KOH extraction process, and 0.1–0.5 mol / L disodium ethylenediaminetetraacetate is added as a complexing agent, with the molar ratio of the complexing agent to the heavy metal ions being 1.2–1.8:

1.

9. The method for preparing the artificial humic acid and carbon dioxide compound fertilizer according to claim 8, characterized in that, Water-soluble potassium humate was obtained by spray drying the supernatant after alkali extraction and separation, and soil remediation agent was obtained by granulation of the residue. The spray drying conditions were: inlet temperature 180–190℃, outlet temperature 85–90℃, and atomization pressure 0.8–1.2MPa.

10. The method for preparing the artificial humic acid and carbon dioxide compound fertilizer according to claim 1, characterized in that, The reaction endpoint for step S4, the preparation of compound carbon fertilizer, is determined based on the following multiple indicators: (i) solution conductivity ≥ 15 mS / cm; (ii) pH drops to 7.2–7.8; (iii) bicarbonate (HCO3) ions... – When the concentration reaches 120–150 mmol / L, the prepared compound carbon fertilizer has the performance indicators of CO2 fixation rate ≥85% and nutrient release period ≥30 days.

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